The present invention relates to an improved structural beam, or bumper, especially for a vehicle, comprising an elongated profile which upon collision is adapted for absorbing collision energy and forces. The bumper is prepared from a complete and hollow blank and is provided with different cross sections along a more or less arched section.
The invention also relates to a method for fabrication of such a structural beam or bumper.
The applicant""s own patent application WO 97/27082 discloses a structural beam or bumper prepared from a complete and hollow blank that is provided with different cross sections along its more or less arched extension. The bumper has a compressed or folded cross section at the areas of each of the terminal portions, while the cross sections at each side of its center are substantially unchanged. The center of the bumper is provided with an outwardly pressed cross section. The manipulated cross section of the bumper contributes to an improved bumper with very good flexing characteristics. Meanwhile, bumpers of this type involving one single chamber will often require the use of quite comprehensive forming operations to achieve the desired shape of the bumper. Further, single chamber beams may be prone to buckling under high loads.
The present invention involves substantial improvements of such a structural beam or bumper and the fabrication thereof.
U.S. Pat. No. 5,340,178 discloses a hollow beam having a reinforcing web of a generally S-shaped configuration interconnecting outer and inner walls of the beam. The beam can be in the shape of a straight tubular section before being formed to a curved or bent configuration. The disclosure does not indicate that the cross section of the beam is manipulated as such, it just indicated that the beam may be curved or have its end portions bent rearwardly. Thus the beam is not provided with different cross sections along its extension and is therefore merely of a constant cross section type beam. Further, the beam configuration is not very suitable for being formed in accordance with the present invention because the S-shaped web will not be able to transmit forces between the outer and inner walls in a sufficient manner during the forming process as compared to that of the present invention.
EP-A-0 687 743 discloses an aluminium alloy bumper-reinforcing material, comprising specified amounts of alloying elements. The figures of the disclosure relate to a bumper having three chambers with its end portions bent rearwardly as such, but the bumper is not manipulated to different cross sections along the extension of the bumper, i.e. the bumper has a constant cross section along its extension.
An object of the present invention is the task of providing an improved bumper which combines the protection of a vehicle and persons in the vehicle upon collision. In addition, it is a further object of the invention to provide an improved method for fabrication of such a bumper.
The invention has as one of its objectives to provide a bumper which excels in high torsional stiffness, combined with great bending softness.
A further objective of the invention is to provide a bumper that allows for rational and sturdy attachment thereof to the frame of the vehicle.
An object of the invention is also to provide an elastic and relatively slender structural beam or bumper, which in relation to previously known profile based, closed bumpers, may absorb more elastic and plastic bending energy per unit quantity of used material.
Further, the invention relates to a method which renders a more rational and simplified production of profile based, closed bumpers, with the method at the same time being specifically favorable for high rate forming in a production line.
These and other objects are achieved in a bumper of the type as stated previously, which relates to a structural beam or bumper, especially for a vehicle. The bumper comprises an elongated profile which upon collision is adapted for absorbing collision energy and forces. The bumper is preferred from a complete and hollow blank, and is further provided with different cross sections along its more or less arched extension. The bumper has an unchanged, or compressed or folded cross section, at the areas of each of the terminal portions, a substantially unchanged basic cross section at each side of its center, and at its center an outwardly pressed cross section relative to the basic cross section. The bumper also has one outer wall portion and one inner wall portion. The bumper is characterized in that at least one part of the interior section of the structural beam or bumper is divided by at least one protrusion or one dividing wall, whereby the interior section of the beam or bumper comprises at least two chambers.
In accordance with the bumper of the instant invention, there is achieved favorable cross sections along the length of the bumper that sustain very good elasticity properties. Further, according to the invention, the manipulated cross section of the bumper may be formed by a simplified forming operation.
A specific embodiment of such a bumper may have a cross section at the center defined by an outer wall portion and an inner wall portion, with the outer wall portion having a larger height than that of the inner wall portion. Slanted yoke portions interconnect the outer wall portion and the inner wall portion. At least one dividing wall extends substantially perpendicularly from the inner wall portion, and the outer wall portion has a concave exterior face. The cross section at each side of the center comprises a less concave, generally flat or convex outer wall portion, an arched inner wall portion, as well as yoke portions extending substantially perpendicularly from the outer wall portion, with the dividing wall extending substantially perpendicularly from the inner wall portion. At each side of the center, the outer wall portion has substantially the same height, or has slightly a larger height than that of the cross section at the center, and the inner wall portion is of lesser height. The cross section at the terminal portions is defined by an outer wall portion having a height as large as that of the cross section at the center, an inner wall portion having a larger height than the height of the inner wall portion at the center of the bumper, and intermediate arched, sharp cornered or wavy yoke portions.
Further, it is appropriate that this type of bumper comprises a closed cross section having an inner wall portion with a relatively large wall thickness compared to that of the dividing wall and the yoke portions, and an outer wall portion provided with a relatively large wall thickness at its upper and lower parts as compared to that of the dividing wall and the yoke portions. Advantageously, the transitions of thickness in the walls of the cross sections of the bumper are smooth.
Further, it is to be understood that the outer wall portion can be substantially straight, or can be provided with a more or less contoured shape.
Further, appropriately, the terminal portions may be so prepared that they merge into attachment portions which are provided with individual grids, or alternatively into net parallel surfaces that can be placed against associated side beams for attachment thereto.
Further, it is to be understood that the bumper may be prepared substantially symmetrically about a central plane extending in the longitudinal direction of the car, and can be provided with an outer mantle of plastic material.
The method for fabrication of a such a structural beam or bumper comprises the use of various forming operations. The beam or bumper is prepared from a complete hollow blank with the interior of the blank being divided by at least one protrusion or one dividing wall. At least in the center portion of the blank, the forming operations result in the dividing wall transmitting forces between the outer and the inner wall of the beam such that the blank is processed to have an outwardly pressed cross section at this portion. In other words, the dividing wall transmits forces in an advantageous manner during the forming operation of the bumper. In crash situations, the dividing wall will be an effective contribution to improve the energy absorbing properties of the bumper.
In one embodiment of the method, the processing of the blank takes place in a first stretching or pressing operation to provide the blank with a main shape, especially a vaguely arched shape in the longitudinal direction of the blank. Thereafter, the blank, at the same time or in subsequent processing operations, is processed at its center portion and compressed at its terminal portions. Preferably, the sections on each side of the center remain unprocessed.
Advantageously, as a blank is used an extruded profile having a closed cross section, with the inner wall portion and the ends of the outer wall portion having relatively larger wall thicknesses than the wall thicknesses of the intermediate yoke portions and the dividing wall, and with the transitions of thickness in the walls of the cross sections of the bumper being smooth. The enlarged thicknesses of the inner and outer walls are particularly advantageous while performing the forming operations on the blank, as these enlarged wall sections can be clamped during the forming operations and thereby improve the ability to manipulate the cross section of the blank to the desired form.
The bumper can be manufactured by outer processing, with the outer processing being performed by mechanical tools. Alternatively, hydroforming can be used.
Further advantages and specific features of the present invention will appear from the following description taken in connection with the attached drawings, as well as from the appended patent claims.